This new project seeks to determine the structure of neuronal and glial cytoplasm particularly as it pertains to axoplasmic transport, secretion, cell movement, and the organization of the cell surface. Living cells or tissues are directly rapid-frozen and the structure of their cytoplasm is determined by one of two methods, freeze-etching or freeze-substitution. Axons in turtle optic nerves have different axoplasmic domains, each characterized by specific types of filaments and by its content of organelles. In other experiments, cultured myocytes grown on grids, frozen, and freeze-substituted are examined directly at high voltages in an electromicroscope. So far, it has been shown that the cytoplasmic anlage consists of fine filaments instead of a microtubular meshwork. We plan to use this direct method of organelles moving by fast axoplasmic transport, and to observe how the cytoskeleton changes near aggregations of receptors at post synaptic membranes in developing synapses.